Wednesday, 13 April 2016

Real Time SQL Server Interview questions and answers

What is normalization? - Well a relational database is
basically composed of tables that contain related data. So the Process of
organizing this data into tables is actually referred to as normalization.

What is a Stored Procedure? - Its nothing but a set of T-SQL
statements combined to perform a single task of several tasks. Its basically
like a Macro so when you invoke the Stored procedure, you actually run a set of
statements.

Can you give an example of Stored Procedure? - sp_helpdb ,
sp_who2, sp_renamedb are a set of system defined stored procedures. We can also
have user defined stored procedures which can be called in similar way.

What is a trigger? - Triggers are basically used to
implement business rules. Triggers is also similar to stored procedures. The
difference is that it can be activated when data is added or edited or deleted
from a table in a database.

What is a view? - If we have several tables in a db and we
want to view only specific columns from specific tables we can go for views. It
would also suffice the needs of security some times allowing specfic users to
see only specific columns based on the permission that we can configure on the
view. Views also reduce the effort that is required for writing queries to
access specific columns every time.

What is an Index? - When queries are run against a db, an
index on that db basically helps in the way the data is sorted to process the
query for faster and data retrievals are much faster when we have an index.

What are the types of indexes available with SQL Server? -
There are basically two types of indexes that we use with the SQL Server.
Clustered and the Non-Clustered.

What is the basic difference between clustered and a
non-clustered index? - The difference is that, Clustered index is unique for
any given table and we can have only one clustered index on a table. The leaf
level of a clustered index is the actual data and the data is resorted in case
of clustered index. Whereas in case of non-clustered index the leaf level is
actually a pointer to the data in rows so we can have as many non-clustered
indexes as we can on the db.

What are cursors? - Well cursors help us to do an operation
on a set of data that we retreive by commands such as Select columns from
table. For example : If we have duplicate records in a table we can remove it
by declaring a cursor which would check the records during retreival one by one
and remove rows which have duplicate values.

When do we use the UPDATE_STATISTICS command? - This command
is basically used when we do a large processing of data. If we do a large
amount of deletions any modification or Bulk Copy into the tables, we need to
basically update the indexes to take these changes into account.
UPDATE_STATISTICS updates the indexes on these tables accordingly.

Which TCP/IP port does SQL Server run on? - SQL Server runs
on port 1433 but we can also change it for better security.

From where can you change the default port? - From the
Network Utility TCP/IP properties –> Port number.both on client and the
server.

Can you tell me the difference between DELETE & TRUNCATE
commands? - Delete command removes the rows from a table based on the condition
that we provide with a WHERE clause. Truncate will actually remove all the rows
from a table and there will be no data in the table after we run the truncate
command.

Can we use Truncate command on a table which is referenced
by FOREIGN KEY? - No. We cannot use Truncate command on a table with Foreign
Key because of referential integrity.

What is the use of DBCC commands? - DBCC stands for database
consistency checker. We use these commands to check the consistency of the
databases, i.e., maintenance, validation task and status checks.

Can you give me some DBCC command options?(Database
consistency check) - DBCC CHECKDB - Ensures that tables in the db and the
indexes are correctly linked.and DBCC CHECKALLOC - To check that all pages in a
db are correctly allocated. DBCC SQLPERF - It gives report on current usage of
transaction log in percentage. DBCC CHECKFILEGROUP - Checks all tables file
group for any damage.

What command do we use to rename a db? - sp_renamedb
‘oldname’ , ‘newname’

Well sometimes sp_reanmedb may not work you know because if
some one is using the db it will not accept this command so what do you think
you can do in such cases? - In such cases we can first bring to db to single
user using sp_dboptions and then we can rename that db and then we can rerun
the sp_dboptions command to remove the single user mode.

What is the difference between a HAVING CLAUSE and a WHERE
CLAUSE? - Having Clause is basically used only with the GROUP BY function in a
query. WHERE Clause is applied to each row before they are part of the GROUP BY
function in a query.

What do you mean by COLLATION? - Collation is basically the
sort order. There are three types of sort order Dictionary case sensitive,
Dictonary - case insensitive and Binary.

What is a Join in SQL Server? - Join actually puts data from
two or more tables into a single result set.

Can you explain the types of Joins that we can have with Sql
Server? - There are three types of joins: Inner Join, Outer Join, Cross Join

When do you use SQL Profiler? - SQL Profiler utility allows
us to basically track connections to the SQL Server and also determine activities
such as which SQL Scripts are running, failed jobs etc..

What is a Linked Server? - Linked Servers is a concept in
SQL Server by which we can add other SQL Server to a Group and query both the
SQL Server dbs using T-SQL Statements.

Can you link only other SQL Servers or any database servers
such as Oracle? - We can link any server provided we have the OLE-DB provider
from Microsoft to allow a link. For Oracle we have a OLE-DB provider for oracle
that microsoft provides to add it as a linked server to the sql server group.

Which stored procedure will you be running to add a linked
server? - sp_addlinkedserver, sp_addlinkedsrvlogin

Can you explain the role of each service? - SQL SERVER - is
for running the databases SQL AGENT - is for automation such as Jobs, DB
Maintanance, Backups DTC - Is for linking and connecting to other SQL Servers

How do you troubleshoot SQL Server if its running very slow?
- First check the processor and memory usage to see that processor is not above
80% utilization and memory not above 40-45% utilization then check the disk
utilization using Performance Monitor, Secondly, use SQL Profiler to check for
the users and current SQL activities and jobs running which might be a problem.
Third would be to run UPDATE_STATISTICS command to update the indexes

Lets say due to N/W or Security issues client is not able to
connect to server or vice versa. How do you troubleshoot? - First I will look
to ensure that port settings are proper on server and client Network utility
for connections. ODBC is properly configured at client end for connection
——Makepipe & readpipe are utilities to check for connection. Makepipe is
run on Server and readpipe on client to check for any connection issues.

Where do you think the users names and passwords will be
stored in sql server? - They get stored in master db in the sysxlogins table.

What is log shipping? Can we do logshipping with SQL Server
7.0 - Logshipping is a new feature of SQL Server 2000. We should have two SQL
Server - Enterprise Editions. From Enterprise Manager we can configure the
logshipping. In logshipping the transactional log file from one server is
automatically updated into the backup database on the other server. If one
server fails, the other server will have the same db and we can use this as the
DR (disaster recovery) plan.

Let us say the SQL Server crashed and you are rebuilding the
databases including the master database what procedure to you follow? - For
restoring the master db we have to stop the SQL Server first and then from
command line we can type SQLSERVER –m which will basically bring it into the
maintenance mode after which we can restore the master db.

Let us say master db itself has no backup. Now you have to
rebuild the db so what kind of action do you take?

What is BCP? When do we use it? - BulkCopy is a tool used to
copy huge amount of data from tables and views. But it won’t copy the
structures of the same.

What should we do to copy the tables, schema and views from
one SQL Server to another? - We have to write some DTS packages for it.

What are the different types of joins and what dies each do?
What are the four main query statements?

----------------------------------PINAL Dave

What is RDBMS?

Relational Data Base Management Systems (RDBMS) are database
management systems that maintain data records and indices in tables.
Relationships may be created and maintained across and among the data and
tables. In a relational database, relationships between data items are
expressed by means of tables. Interdependencies among these tables are
expressed by data values rather than by pointers. This allows a high degree of
data independence. An RDBMS has the capability to recombine the data items from
different files, providing powerful tools for data usage.

What is normalization?

Database normalization is a data design and organization
process applied to data structures based on rules that help build relational
databases. In relational database design, the process of organizing data to
minimize redundancy. Normalization usually involves dividing a database into
two or more tables and defining relationships between the tables. The objective
is to isolate data so that additions, deletions, and modifications of a field
can be made in just one table and then propagated through the rest of the
database via the defined relationships.

What is Stored Procedure?

A stored procedure is a named group of SQL statements that
have been previously created and stored in the server database. Stored
procedures accept input parameters so that a single procedure can be used over
the network by several clients using different input data. And when the
procedure is modified, all clients automatically get the new version. Stored
procedures reduce network traffic and improve performance. Stored procedures can
be used to help ensure the integrity of the database.

e.g. sp_helpdb, sp_renamedb, sp_depends etc.

What is Trigger?

A trigger is a SQL procedure that initiates an action when
an event (INSERT, DELETE or UPDATE) occurs. Triggers are stored in and managed
by the DBMS.Triggers are used to maintain the referential integrity of data by
changing the data in a systematic fashion. A trigger cannot be called or
executed; the DBMS automatically fires the trigger as a result of a data
modification to the associated table. Triggers can be viewed as similar to
stored procedures in that both consist of procedural logic that is stored at
the database level. Stored procedures, however, are not event-drive and are not
attached to a specific table as triggers are. Stored procedures are explicitly
executed by invoking a CALL to the procedure while triggers are implicitly
executed. In addition, triggers can also execute stored procedures.

Nested Trigger: A trigger can also contain INSERT, UPDATE
and DELETE logic within itself, so when the trigger is fired because of data
modification it can also cause another data modification, thereby firing
another trigger. A trigger that contains data modification logic within itself
is called a nested trigger.

What is View?

A simple view can be thought of as a subset of a table. It
can be used for retrieving data, as well as updating or deleting rows. Rows
updated or deleted in the view are updated or deleted in the table the view was
created with. It should also be noted that as data in the original table
changes, so does data in the view, as views are the way to look at part of the
original table. The results of using a view are not permanently stored in the
database. The data accessed through a view is actually constructed using
standard T-SQL select command and can come from one to many different base
tables or even other views.

What is Index?

An index is a physical structure containing pointers to the
data. Indices are created in an existing table to locate rows more quickly and
efficiently. It is possible to create an index on one or more columns of a
table, and each index is given a name. The users cannot see the indexes, they
are just used to speed up queries. Effective indexes are one of the best ways
to improve performance in a database application. A table scan happens when
there is no index available to help a query. In a table scan SQL Server
examines every row in the table to satisfy the query results. Table scans are
sometimes unavoidable, but on large tables, scans have a terrific impact on
performance.

Clustered indexes define the physical sorting of a database
table’s rows in the storage media. For this reason, each database table may
have only one clustered index.

Non-clustered indexes are created outside of the database
table and contain a sorted list of references to the table itself.

What is the difference between clustered and a non-clustered
index?

A clustered index is a special type of index that reorders
the way records in the table are physically stored. Therefore table can have
only one clustered index. The leaf nodes of a clustered index contain the data
pages.

A nonclustered index is a special type of index in which the
logical order of the index does not match the physical stored order of the rows
on disk. The leaf node of a nonclustered index does not consist of the data
pages. Instead, the leaf nodes contain index rows.

What are the different index configurations a table can
have?

A table can have one of the following index configurations:

No indexes

A clustered index

A clustered index and many nonclustered indexes

A nonclustered index

Many nonclustered indexes

What is cursors?

Cursor is a database object used by applications to
manipulate data in a set on a row-by-row basis, instead of the typical SQL
commands that operate on all the rows in the set at one time.

In order to work with a cursor we need to perform some steps
in the following order:

Declare cursor

Open cursor

Fetch row from the cursor

Process fetched row

Close cursor

Deallocate cursor

What is the use of DBCC commands?

DBCC stands for database consistency checker. We use these
commands to check the consistency of the databases, i.e., maintenance,
validation task and status checks.

E.g. DBCC CHECKDB - Ensures that tables in the db and the
indexes are correctly linked.

DBCC CHECKALLOC - To check that all pages in a db are
correctly allocated.

DBCC CHECKFILEGROUP - Checks all tables file group for any
damage.

What is a Linked Server?

Linked Servers is a concept in SQL Server by which we can
add other SQL Server to a Group and query both the SQL Server dbs using T-SQL
Statements. With a linked server, you can create very clean, easy to follow,
SQL statements that allow remote data to be retrieved, joined and combined with
local data.

Storped Procedure sp_addlinkedserver, sp_addlinkedsrvlogin
will be used add new Linked Server.

What is Collation?

Collation refers to a set of rules that determine how data
is sorted and compared. Character data is sorted using rules that define the
correct character sequence, with options for specifying case-sensitivity,
accent marks, kana character types and character width.

What are different type of Collation Sensitivity?

Case sensitivity

A and a, B and b, etc.

Accent sensitivity

a and á, o and ó, etc.

Kana Sensitivity

When Japanese kana characters Hiragana and Katakana are
treated differently, it is called Kana sensitive.

Width sensitivity

When a single-byte character (half-width) and the same
character when represented as a double-byte character (full-width) are treated
differently then it is width sensitive.

What’s the difference between a primary key and a unique
key?

Both primary key and unique enforce uniqueness of the column
on which they are defined. But by default primary key creates a clustered index
on the column, where are unique creates a nonclustered index by default.
Another major difference is that, primary key doesn’t allow NULLs, but unique
key allows one NULL only.

How to implement one-to-one, one-to-many and many-to-many
relationships while designing tables?

One-to-One relationship can be implemented as a single table
and rarely as two tables with primary and foreign key relationships.

One-to-Many relationships are implemented by splitting the
data into two tables with primary key and foreign key relationships.

Many-to-Many relationships are implemented using a junction
table with the keys from both the tables forming the composite primary key of
the junction table.

What is a NOLOCK?

Using the NOLOCK query optimiser hint is generally
considered good practice in order to improve concurrency on a busy system. When
the NOLOCK hint is included in a SELECT statement, no locks are taken when data
is read. The result is a Dirty Read, which means that another process could be
updating the data at the exact time you are reading it. There are no guarantees
that your query will retrieve the most recent data. The advantage to
performance is that your reading of data will not block updates from taking
place, and updates will not block your reading of data. SELECT statements take
Shared (Read) locks. This means that multiple SELECT statements are allowed
simultaneous access, but other processes are blocked from modifying the data.
The updates will queue until all the reads have completed, and reads requested
after the update will wait for the updates to complete. The result to your
system is delay(blocking).

What is difference between DELETE & TRUNCATE commands?

Delete command removes the rows from a table based on the
condition that we provide with a WHERE clause. Truncate will actually remove
all the rows from a table and there will be no data in the table after we run
the truncate command.

TRUNCATE

TRUNCATE is faster and uses fewer system and transaction log
resources than DELETE.

TRUNCATE removes the data by deallocating the data pages
used to store the table’s data, and only the page deallocations are recorded in
the transaction log.

TRUNCATE removes all rows from a table, but the table
structure and its columns, constraints, indexes and so on remain. The counter
used by an identity for new rows is reset to the seed for the column.

You cannot use TRUNCATE TABLE on a table referenced by a
FOREIGN KEY constraint.

Because TRUNCATE TABLE is not logged, it cannot activate a
trigger.

TRUNCATE can not be Rolled back using logs.

TRUNCATE is DDL Command.

TRUNCATE Resets identity of the table.

DELETE

DELETE removes rows one at a time and records an entry in
the transaction log for each deleted row.

If you want to retain the identity counter, use DELETE
instead. If you want to remove table definition and its data, use the DROP
TABLE statement.

DELETE Can be used with or without a WHERE clause

DELETE Activates Triggers.

DELETE Can be Rolled back using logs.

DELETE is DML Command.

DELETE does not reset identity of the table.

Difference between Function and Stored Procedure?

UDF can be used in the SQL statements anywhere in the
WHERE/HAVING/SELECT section where as Stored procedures cannot be.

UDFs that return tables can be treated as another rowset.
This can be used in JOINs with other tables.

Inline UDF’s can be though of as views that take parameters
and can be used in JOINs and other Rowset operations.

When is the use of UPDATE_STATISTICS command?

This command is basically used when a large processing of
data has occurred. If a large amount of deletions any modification or Bulk Copy
into the tables has occurred, it has to update the indexes to take these
changes into account. UPDATE_STATISTICS updates the indexes on these tables
accordingly.

What types of Joins are possible with Sql Server?

Joins are used in queries to explain how different tables
are related. Joins also let you select data from a table depending upon data
from another table.

Types of joins: INNER JOINs, OUTER JOINs, CROSS JOINs. OUTER
JOINs are further classified as LEFT OUTER JOINS, RIGHT OUTER JOINS and FULL
OUTER JOINS.

What is the difference between a HAVING CLAUSE and a WHERE
CLAUSE?

Specifies a search condition for a group or an aggregate.
HAVING can be used only with the SELECT statement. HAVING is typically used in
a GROUP BY clause. When GROUP BY is not used, HAVING behaves like a WHERE
clause. Having Clause is basically used only with the GROUP BY function in a
query. WHERE Clause is applied to each row before they are part of the GROUP BY
function in a query. HAVING criteria is applied after the the grouping of rows
has occurred.

What is sub-query? Explain properties of sub-query.

Sub-queries are often referred to as sub-selects, as they
allow a SELECT statement to be executed arbitrarily within the body of another
SQL statement. A sub-query is executed by enclosing it in a set of parentheses.
Sub-queries are generally used to return a single row as an atomic value,
though they may be used to compare values against multiple rows with the IN
keyword.

A subquery is a SELECT statement that is nested within
another T-SQL statement. A subquery SELECT statement if executed independently
of the T-SQL statement, in which it is nested, will return a result set.
Meaning a subquery SELECT statement can standalone and is not depended on the
statement in which it is nested. A subquery SELECT statement can return any
number of values, and can be found in, the column list of a SELECT statement, a
FROM, GROUP BY, HAVING, and/or ORDER BY clauses of a T-SQL statement. A
Subquery can also be used as a parameter to a function call. Basically a
subquery can be used anywhere an expression can be used.

Properties of Sub-Query

A subquery must be enclosed in the parenthesis.

A subquery must be put in the right hand of the comparison
operator, and

User-Defined Functions allow to define its own T-SQL
functions that can accept 0 or more parameters and return a single scalar data
value or a table data type.

What kind of User-Defined Functions can be created?

There are three types of User-Defined functions in SQL
Server 2000 and they are Scalar, Inline Table-Valued and Multi-statement
Table-valued.

Scalar User-Defined Function

A Scalar user-defined function returns one of the scalar
data types. Text, ntext, image and timestamp data types are not supported.
These are the type of user-defined functions that most developers are used to
in other programming languages. You pass in 0 to many parameters and you get a
return value.

Inline Table-Value User-Defined Function

An Inline Table-Value user-defined function returns a table
data type and is an exceptional alternative to a view as the user-defined
function can pass parameters into a T-SQL select command and in essence provide
us with a parameterized, non-updateable view of the underlying tables.

Multi-statement Table-Value User-Defined Function

A Multi-Statement Table-Value user-defined function returns
a table and is also an exceptional alternative to a view as the function can
support multiple T-SQL statements to build the final result where the view is
limited to a single SELECT statement. Also, the ability to pass parameters into
a T-SQL select command or a group of them gives us the capability to in essence
create a parameterized, non-updateable view of the data in the underlying
tables. Within the create function command you must define the table structure
that is being returned. After creating this type of user-defined function, It
can be used in the FROM clause of a T-SQL command unlike the behavior found
when using a stored procedure which can also return record sets.

Which TCP/IP port does SQL Server run on? How can it be
changed?

SQL Server runs on port 1433. It can be changed from the
Network Utility TCP/IP properties –> Port number.both on client and the
server.

What are the authentication modes in SQL Server? How can it
be changed?

SQL Server agent plays an important role in the day-to-day
tasks of a database administrator (DBA). It is often overlooked as one of the
main tools for SQL Server management. Its purpose is to ease the implementation
of tasks for the DBA, with its full-function scheduling engine, which allows
you to schedule your own jobs and scripts.

Can a stored procedure call itself or recursive stored
procedure? How many level SP nesting possible?

Yes. Because Transact-SQL supports recursion, you can write
stored procedures that call themselves. Recursion can be defined as a method of
problem solving wherein the solution is arrived at by repetitively applying it
to subsets of the problem. A common application of recursive logic is to
perform numeric computations that lend themselves to repetitive evaluation by
the same processing steps. Stored procedures are nested when one stored
procedure calls another or executes managed code by referencing a CLR routine,
type, or aggregate. You can nest stored procedures and managed code references
up to 32 levels.

What is @@ERROR?

The @@ERROR automatic variable returns the error code of the
last Transact-SQL statement. If there was no error, @@ERROR returns zero.
Because @@ERROR is reset after each Transact-SQL statement, it must be saved to
a variable if it is needed to process it further after checking it.

Log shipping is the process of automating the backup of
database and transaction log files on a production SQL server, and then
restoring them onto a standby server. Enterprise Editions only supports log
shipping. In log shipping the transactional log file from one server is
automatically updated into the backup database on the other server. If one
server fails, the other server will have the same db can be used this as the
Disaster Recovery plan. The key feature of log shipping is that is will
automatically backup transaction logs throughout the day and automatically
restore them on the standby server at defined interval.

What is the difference between a local and a global
variable?

A local temporary table exists only for the duration of a
connection or, if defined inside a compound statement, for the duration of the
compound statement.

A global temporary table remains in the database
permanently, but the rows exist only within a given connection. When connection
are closed, the data in the global temporary table disappears. However, the
table definition remains with the database for access when database is opened
next time

What command do we use to rename a db?

sp_renamedb ‘oldname’ , ‘newname’

If someone is using db it will not accept sp_renmaedb. In
that case first bring db to single user using sp_dboptions. Use sp_renamedb to
rename database. Use sp_dboptions to bring database to multi user mode.

What is sp_configure commands and set commands?

Use sp_configure to display or change server-level settings.
To change database-level settings, use ALTER DATABASE. To change settings that
affect only the current user session, use the SET statement.

Using query analyzer, name 3 ways to get an accurate count
of the number of records in a table?

Primary keys are the unique identifiers for each row. They
must contain unique values and cannot be null. Due to their importance in
relational databases, Primary keys are the most fundamental of all keys and
constraints. A table can have only one Primary key.

Foreign keys are both a method of ensuring data integrity
and a manifestation of the relationship between tables.

What is data integrity? Explain constraints?

Data integrity is an important feature in SQL Server. When
used properly, it ensures that data is accurate, correct, and valid. It also
acts as a trap for otherwise undetectable bugs within applications.

A PRIMARY KEY constraint is a unique identifier for a row
within a database table. Every table should have a primary key constraint to
uniquely identify each row and only one primary key constraint can be created
for each table. The primary key constraints are used to enforce entity
integrity.

A UNIQUE constraint enforces the uniqueness of the values in
a set of columns, so no duplicate values are entered. The unique key
constraints are used to enforce entity integrity as the primary key
constraints.

A FOREIGN KEY constraint prevents any actions that would
destroy links between tables with the corresponding data values. A foreign key
in one table points to a primary key in another table. Foreign keys prevent
actions that would leave rows with foreign key values when there are no primary
keys with that value. The foreign key constraints are used to enforce
referential integrity.

A CHECK constraint is used to limit the values that can be
placed in a column. The check constraints are used to enforce domain integrity.

A NOT NULL constraint enforces that the column will not
accept null values. The not null constraints are used to enforce domain
integrity, as the check constraints.

How to get @@error and @@rowcount at the same time?

If @@Rowcount is checked after Error checking statement then
it will have 0 as the value of @@Recordcount as it would have been reset.

And if @@Recordcount is checked before the error-checking
statement then @@Error would get reset. To get @@error and @@rowcount at the
same time do both in same statement and store them in local variable. SELECT
@RC = @@ROWCOUNT, @ER = @@ERROR

What is Identity?

Identity (or AutoNumber) is a column that automatically
generates numeric values. A start and increment value can be set, but most DBA
leave these at 1. A GUID column also generates numbers, the value of this
cannot be controled. Identity/GUID columns do not need to be indexed.

What is BCP? When does it used?

BulkCopy is a tool used to copy huge amount of data from tables
and views. BCP does not copy the structures same as source to destination.

How do you load large data to the SQL server database?

BulkCopy is a tool used to copy huge amount of data from
tables. BULK INSERT command helps to Imports a data file into a database table
or view in a user-specified format.

Can we rewrite subqueries into simple select statements or
with joins?

Subqueries can often be re-written to use a standard outer
join, resulting in faster performance. As we may know, an outer join uses the
plus sign (+) operator to tell the database to return all non-matching rows
with NULL values. Hence we combine the outer join with a NULL test in the WHERE
clause to reproduce the result set without using a sub-query.

Can SQL Servers linked to other servers like Oracle?

SQL Server can be lined to any server provided it has OLE-DB
provider from Microsoft to allow a link. E.g. Oracle has a OLE-DB provider for
oracle that Microsoft provides to add it as linked server to SQL Server group.

How to know which index a table is using?

SELECT table_name,index_name FROM user_constraints

How to copy the tables, schema and views from one SQL server
to another?

Microsoft SQL Server 2000 Data Transformation Services (DTS)
is a set of graphical tools and programmable objects that lets user extract,
transform, and consolidate data from disparate sources into single or multiple
destinations.

What is Self Join?

This is a particular case when one table joins to itself,
with one or two aliases to avoid confusion. A self join can be of any type, as
long as the joined tables are the same. A self join is rather unique in that it
involves a relationship with only one table. The common example is when company
have a hierarchal reporting structure whereby one member of staff reports to
another.

What is Cross Join?

A cross join that does not have a WHERE clause produces the
Cartesian product of the tables involved in the join. The size of a Cartesian
product result set is the number of rows in the first table multiplied by the
number of rows in the second table. The common example is when company wants to
combine each product with a pricing table to analyze each product at each
price.